The present invention relates to a method and a system for controlling a stand-by braking torque applied to an automotive vehicle under a condition of approaching or following an obstacle preceding the vehicle. The term xe2x80x9cobstaclexe2x80x9d is used herein to mean a stationary or moving object within the path of the vehicle, for example, vehicles, pedestrians, etc. The term xe2x80x9cstand-by braking torquexe2x80x9d is used herein to mean a brake torque, i.e., a negative torque, applied to a vehicle in anticipation of operator braking action or when operator braking action is imminent under a condition of approaching or following an obstacle preceding the vehicle, The term xe2x80x9coperator braking actionxe2x80x9d is used herein to mean vehicle operator or driver action to operate a brake pedal with intention to lower traveling speed of a vehicle.
JP-A 7-144588 discloses a system whereby traveling speed and deceleration of an obstacle preceding a host vehicle are determined using a Doppler sensor and a vehicle speed sensor, which are on the vehicle, and a desired distance from the obstacle is determined. In this system, a vehicle operator is warned and an automatic braking action is initiated if the distance from the obstacle becomes less than the desired distance.
JP-A 6-24302 discloses a system whereby, when operator foot leaves an accelerator pedal, two micro switches are both closed to energize a solenoid for activating a brake pedal. Energizing the solenoid pulls the brake pedal to partially activate a braking system before operator braking action.
Other systems have been proposed that are intended to initiate braking action before operator braking action. JP-A 8-80822 discloses a system whereby, when the time rate of change of an accelerator angle upon operator releasing the accelerator pedal exceeds a predetermined level, a brake actuator is activated to partially activate a braking system before operator braking action.
JP-A 10-59150 discloses a system whereby, when the time rate of change of a throttle angle upon operator releasing an accelerator pedal exceeds a predetermined level, a support braking torque is applied to wheels of an automotive vehicle in addition to braking torque applied to the vehicle wheels corresponding to depression of a brake pedal by vehicle operator.
JP-A 11-321591 discloses a system, whereby clearance between brake pad and lining of an automotive vehicle is decreased when pressure with which an accelerator pedal is depressed is decreased or the accelerator pedal is released, thereby to shorten time and distance for vehicle operator to stop the vehicle.
In the event where brake pressure is regulated to apply stand-by braking torque, a need remains toward a control strategy for brake pressure that may be used with conventional widely prevailing brake components.
An object of the present invention is to meet the above-mentioned need by providing a method or system for controlling brake pressure, which does not rely on feedback control.
The present invention provides a method for controlling a stand-by braking torque applied to an automotive vehicle under a condition of approaching or following an obstacle preceding the vehicle, the method comprising:
determining a brake signal for brake pressure to apply a brake torque, as a stand-by braking torque;
establishing at least one brake torque threshold;
monitoring the brake torque;
comparing the monitored brake torque with the established brake torque threshold; and
modifying the brake signal in response to the comparing the monitored brake torque with the established brake torque threshold.